Most existing electron sources extract electrons from conductors. There are several disadvantages associated with currently-available electron beam sources. The Fermi temperature of the extracted electrons is significantly lower than the electrons remaining in the source, so the electron degeneracy δf (brightness in inverse Compton wavelength units) is close to 1, the maximum allowed by the Pauli exclusion principle. Other factors conspire together to reduce δf many orders of magnitude during extraction. Interactions with the collective electric field (space charge) and with randomly positioned electrons in the beam further decrease the beam brightness. In the case of field emitters, large inhomogeneities in the electric field near the tip also degrade brightness considerably. For example, a state of the art room-temperature field-emitter can produce a DC beam with δf≈10−5, while high-current pulsed RF photoinjector sources for high-energy accelerators strive to produce a beam with δf=2.5×10−12, both significantly lower than the theoretical limit.
Herein, a new concept is described for building a novel electron source designed to produce a pulsed beam with δf≈0.6 and longitudinal emittance four orders of magnitude smaller than currently achieved values. This high brightness, low longitudinal emittance pulsed electron source enables a wide range of novel applications that utilize angstrom-scale spatial resolution and μeV-scale energy resolution.